Low temperature tertiary amine accelerators

ABSTRACT

LOW TEMPERATURE EPOXY CURING ACCELERATORS ARE PREPARED FROM TERTIARY AMINE SALTS OF HYDROBROMIC ACID, PARATOLUENE SULFONIC ACID, 2-ETHYLHEXOIC ACID OR THIOCYANIC ACID, WHEREIN THE TERTIARY AMINE IS EITHER TRIETHYLENE DIAMINE, METHYL TRIETHYLENE OR 2 - ETHYL - 4 - METHYL IMIDAZOLE.

United States atet 3,642,649 LOW TEMPERATURE TERTIARY AMINE ACCELERATORS Harold A. Green, Havel-town, and Robert G. Petrella,

Philadelphia, Pa., assignors to Air Products and Chemicals, Inc., Philadelphia, Pa. No Drawing. Filed Apr. 18, 1969, Ser. No. 818,470 Int. Cl. C08f 45/72; C08g 51/84 US. Cl. 252-182 9 Claims ABSTRACT OF THE DISCLOSURE Low temperature epoxy curing accelerators are prepared from tertiary amine salts of hydrobromic acid, paratoluene sulfonic acid, 2-ethylhexoic acid or thiocyanic acid, wherein the tertiary amine is either triethylene diamine, methyl triethylene diamine or 2 ethyl 4 methyl imidazole.

BACKGROUND OF THE INVENTION The present invention relates to epoxy curing accelerators and the use of said accelerators. More particularly, the present invention relates to certain tertiary amine salts of hydrobromic acid, paratoluene sulfonic acid, 2- ethylhexoic acid or thiocyanic acid which will accelerate the curing of epoxy resins at low temperatures.

Since epoxy compositions for flooring and maintenance coating applications can be formulated for specific applications which require properties such as ease of maintenance, high compressive strength, skid resistance, abrasion resistance and good chemical resistance, epoxy flooring and maintenance coating formulations have been used extensively in dairies, food processing plants, industrial and chemical plants, breweries, bakeries, hotel and hospital kitchens, cafeterias, high-rise construction, airports and other public buildings. For these applications, the property of low temperature curing is a desirable characteristic in the epoxy flooring or maintenance coating system which is utilized.

It is known that acid anhydrides show little activity as curing agents for epoxy resins at either room temperature or at slightly elevated temperatures. Instead, acid anhydrides are effective only at very high temperatures and even then in many cases they act very slowly. It has been proposed that tertiary amines be used as curing accelerators for the acid anhydrides, but this has not overcome all of the problems involved. For example, many of the amine accelerators speed the curing operation at higher temperatures but do not permit the use of lower cure temperatures. In other cases, the presence of the accelerator has a detrimental effect on the properties of the resulting product. Moreover, anhydride curing agents are considered capable of causing severe eye and skin irritation, even burns, depending on the severity of contact.

Known low temperature epoxy curing agents, such as polyamines and polymercaptans, not only have the drawback of being odorous, but present a high dermatitis hazard. In general, the order of dermatitis hazard ranges from a severe hazard with mercaptans to a lower potential hazard with modified amines, amido-amines and polyamides. Aliphatic amines, for example, are skin irritants. They are not only capable of causing dematitis, but are capable of sensitizing some individuals so that even very brief exposure becomes toxic. Edema or even necrosis may result. Aromatic amines, while less irritating to the skin and less prone to cause skin sensitization responses, present a very serious hazard if acquired internally.

SUMMARY OF THE INVENTION An object of the present invention is to provide a low temperature epoxy curing system.

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Another object of the present invention is to provide certain tertiary amine salts of hydrobromic acid, paratoluene sulfonic acid, 2-ethylhexoic acid or thiocyanic acid which will accelerate epoxy curing agents in a manner such that epoxy resins are cured at a practical and acceptable rate at temperatures as low as 35 F.

Still another object of the present invention is to provide low temperature epoxy curing systems for epoxy maintenance coating and flooring applications which will result in superior properties in the resulting coating film.

Yet another object of the present invention is to provide low temperature epoxy curing systems which present a relatively low dermatitis hazard.

These, and other objects of the present invention, are accomplished by preparing certain tertiary amine salts of hydrobromic acid, paratoluene sulfonic acid, 2- ethylhexoic acid or thiocyanic acid and using these salts to accelerate the curing of epoxy resin formulations which employ amido-amine, modified amine, or polyamide curing agents. Tertiary amines which have been discovered to be particularly effective are triethylene diamine, methyl triethylene diamine and 2-ethyl-4-methyl imidazole.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Epoxide Viscosity Resin equivalent (poises) Epon 820 185-205 40-100 Epon 826 180-18 -95 Epon 828. 185-192 -160 Epon 1001. 425-550 1 Solid Epon 1002 600-700 1 Solid Epon 1004- 875-1, 025 1 Solid Araldite 741 x 75 450-530 46-93 Araldite 507 185-192 5-7 Araldite 6005---- 182-190 70-100 Araldlte 6010 185-196 -160 1 At room temperature.

2 75% solids in xylene. In general, epoxy resins which find application in fioorings have an epoxide equivalent ranging between -210. Typically, two types of the low viscosity epoxy resins are used for flooring applications. One type is the highly refined epoxy resin that contains a minimum amount of high molecular weight fractions, e.g., Epon 826; while the other type contains monoepoxide diluents such as phenyl glycidyl ether and butyl glycidyl ether, e.g., Epon 820. Epoxy resins which find application in maintenance coatings have an epoxide equivalent ranging between 425 and 900.

Curing agents for epoxy flooring and maintenance coatings of the present system include amido-amines, modified amines and polyamides. For example, suitable commercial curing agents such as the Pentamids may be employed. Pentamids are polyamides obtained by the condensation of polymerized fatty acid and polyamine. Typical properties of various Pentamids are shown below:

Pentamids are relatively non-toxic and are not classified as skin sensitizers.

Another curing agent which may be used in the present invention is sold by Ciba Products Company under the trademark. Araldite Hardener 956. This curing agent is a low viscosity, modified amine hardener which exhibits low irritation and skin sensitizing effects on contact. The characteristics of Araldite Hardener 956 are set forth below:

Viscosity, centipoises, at 25 C.300-600 Amine nitrogen value, percent23.5-27 .0 Color, Gardner7 max.

Flash point, open cup350 F. (average) Weight per gallon, pounds-8.8 (average) Another curing agent which may be employed is sold by Ciba Products Company under the trademark Araldite Hardener 955 which is a modified liquid amidoamine hardener having the following characteristics.

Viscosity, centipoises, at 25 C.--500900 Equivalent weight (approx.)--65 Weight per gallon, pounds8.2 Flash point, open cup-300 F.

A solvent blend comprising a 2 to 1 mixture of nitropropane and methanol has been found to be particularly effective for maintaining salts of triethylene diamine in solution with an amide-amine curing agent (Hardener 955) and preventing the precipitation of triethylene diamine or triethylene diamine salt. In addition, it has been found that the stability of mixtures of Hardener 955 and the thiocyanic acid salt of triethylene diamine can be improved, with no loss in activity, from a period of 3 to 4 days to a period in excess of 90 days, by the addition of 5 to parts per hundred parts of resin of a low viscosity, i.e., less than about 70 poises at C., polyamide such as Pentamid 840.

Curing agents such as the commercially available Epi- Cure 855 (amido-amine) and Epi-Cure 872 (25:10 ratio by weight of amide-amine and modified amine) may also be employed. The characteristics of these curing agents are set forth below:

The accelerators of the present invention can be prepared by reacting oertain tertiary amines, e.g., triethylene diamine, methyl triethylene diamine and 2-ethyl-4-methyl imidazole, with hydrobromic acid, paratoluene sulfonic acid, 2-ethylhexoic acid or thiocyanic acid. The reaction is carried out in standard fashion with proper care simply by reacting the appropriate quantities of the acid and the amine base. When ammonium thiocyanate is employed as the precursor of the thiocyanic acid the reaction is carried out in a solvent, such as water. Other solvents, such as hexane for methyl triethylene diamine, may be used, but are not preferred. The resulting solvent mixture is then heated to and maintained at reflux conditionspreferably until the evolution of ammonia ceases. The desired tertiary amine salt of hydrobromic acid, para-toluene sulfonic acid, Z-ethylhexoic acid or thiocyanic acid is recovered directly as product or as the residue after evaporating the solvent. Recrystallization from isopropanol or n-butanol or mixtures thereof, may be employed.

The tertiary amine salts of hydrobromic acid, paratoluene sulfonic acid, 2-ethylhexoic acid or thiocyanic acid are used to accelerate the curing of polyepoxides by simply admixing the above-identified accelerators with the curing agent and the polyepoxide. The accelerator and curing agent should be combined together before they are added to the polyepoxide to avoid possible irregular cur- FLOORING FORMULATIONS Ratio of Amount of Accelaccelerator to curing agent erator 1 Curing agent curing agent employed (phr.

Amide-amine or 0.15:1 to 0.73: 1- 11-50.

modified amine. 1 or 2 Polyamide 0.08: 1 to 0.24:1 to (preferred (preferred range range 40 to 65). 0.1: 1 to 0.1521). Amidn-amine or 0.36: 1 to 0.072: 1 11-50.

modified amine. (preferred range 3 0.04:1to 0.06:1).

Polyamide 0.01: 1 to 0.15:1- 35 to 90 (preferred range 40 to 65).

1 1=Methyl triethylene diamine salts; 2=Triethylene diamine salts; 3= Z-ethyl-i-methyl imidazoie salts.

2 Absolute ratio.

3 phr=Parts based on parts of epoxy resin.

MAINTENANCE COATINGS Ratio of accelerator Amount of curing Accelerator Curing agent to curing agent 2 agent employed 3 Amide-amine..- 0.1:1-0.35:1 70-150.

1 Modified amine-" 0.10:1-0.54:1 70-150. Polyarnide 0.1:1-0.3:1 70-150. Amido-amine 1:2-lzl0 (preferred 70-140 (preferred range lat-1:6). range 90-120).

2 Modified amine 0.16:1-0.56;1 70-150.

Polyamide 1:2-1zl2 (preferred 75-150 (preferred range 1:4-lz6). range 90-120). Amido-amine 0.0l7:10.12:1 70-150.

3 Modified amine- 0.036:10.12:1 70-150.

Polyamide 0.01:10.15:1 70-160.

1 1=Methyl triethylene diamine salts; 2=Tr1ethylene diamine salts; 3= 2-ethyl-4-methyl imidazole salts.

2 Absolute ratio.

3 Percent of concentration recommended by manufacturer.

Polyepoxides may be cured with the low temperature epoxy curing system of the present invention over a wide range of temperatures. For example, the tertiary amine salts of the present invention will act to accelerate the epoxy curing agents in a manner such that epoxy resins are cured at a practical and acceptable rate at temperatures as low as 35 F. Curing may also be accomplished by merely mixing the accelerator-curing agent combination together with the polyepoxide, as indicated above, and then letting the mixture stand at room temperature. In some applications, however, it may be desirable to effect a more rapid cure and this may be accomplished by raising the temperature for those applications where heating is permissible.

It has been discovered that extremely rapid curing is obtained using either triethylene diamine or methyl triethylene diamine as the tertiary amine and including 0.3 to 2.4 parts of water per hundred parts of the resin, with a preferred range of 0.4 to 0.9 part of water per hundred parts of resin.

The epoxy flooring compositions of the present invention can be applied using established techniques to a variety of substrates, such as concrete, steel, wood, bituminous asphalt, tile and terrazzo, and then permitted to cure.

Finely divided material, such as silica flour, talc, and calcium carbonate, can be used as filler. The amount of filler can be varied to obtain the desired viscosity. For

flooring applications, however, between 400 and 600 phr. of graded sand may be added. The use of aggregates, such as silica, limestone, granite, etc., can be used to modify the strength, loading capacity, chemical resistance, appearance and wearing characteristics of epoxy flooring.

Maintenance coatings find particular application where a tough and impervious surface is desired. A variety of means, such as, spraying, dipping, brushing, roller coating, etc., can be employed to apply the maintenance coatings. Often it is desirable to include a corrosive resistance pigment in the maintenance coating compositions. Examples of pigments which may be used include lead chromate, basic lead silico-chromate, zinc oxide, and iron oxide.

Reactive diluents include butyl glycidyl ether and phenyl glycidyl ether. However, no reactive diluent is completely free of skin sensitizing properties. Non-reactive diluents include pine oil and di-butyl phthalate. Generally, the total quantity of non-reactive diluent employed is greater than phr., but less than 30 phr.with to phr. normally being preferred.

Solvents may be added for achieving the desired fluidity. They may be volatile solvents which evaporate before or during the curing, e.g., ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone; esters such as ethyl acetate, butyl acetate, ethylene glycol monoethyl ether acetate and ethylene glycol monomethyl ether acetate; and chlorinated hydrocarbons such as trichloropropane and chloroform.

Diethyl phthalate, dibutyl phthalate and adiponitrile are examples of plasticizers which can be used.

It will be understood that various other known additives, including fibrous materials, dyes and resins, may be used with the epoxy flooring and maintenance coatings of the present invention.

The invention will be illustrated by the following spe cific examples, it being understood that there is no intention to be necessarily limited by any details thereof since variations can be made Within the scope of the invention.

Example 1 The triethylene diamine salt of thiocyanic acid was prepared by adding 113.1 grams (1.01 mols) of triethylene diamine to a three-neck liter flask equipped with a magnetic stirring bar. 181.3 grams of distilled water was added to dissolve the triethylene diamine.

A solution of 78.1 grams (1.03 mols) of NH SCN dissolved in 127.2 grams of distilled water was added to the flask from a beaker. The beaker was then rinsed with 54.0 grams of distilled water, which was also added to the flask. The combined weight of the flask and ingredients was 877.4 grams.

After refluxing for 6 hours at 104 C., the flask was cooled and weighed. The total weight of the flask and ingredients was 859.3 grams. The weight loss of 17.6 grams is equivalent to a loss of 1.03 mols of ammonia. The water was then driven off, leaving the triethylene diamine salt of thiocyanic acid.

Example 2 113.0 grams (1.01 mols) of triethylene diamine were dissolved in 140.4 grams of distilled water and added to a tared three-neck liter flask. A solution containing 77.3 grams (1.01 mols) of ammonium thiocyanate dissolved in 108.7 grams of water was added and the mixture was heated to reflux conditions.

When the evolution of NH ceased, the reaction mixture was poured into an evaporating dish. The solid triethylene diamine salt of thiocyanic acid was recrystallized from n-butanol and analyzed.

Analytical data Theoretical (percent): C, 49.16; H, 7.65; N, 24.54; S, 18.72. Actual (percent): C, 48.70; H, 7.67; N, 24.45; S, 18.7.

Example 3 The triethylene diamine salt of dithiocyanic acid was prepared by adding 112 grams (1.0 mol) of triethylene diamine to a three-neck flask equipped with a reflux condenser and an additional funnel. 201 grams of water were added and the mixture stirred until the triethylene diamine becomes dissolved.

Two moles of ammonium thiocyanate dissolved in 265 grams of distilled water were then added to the flask at a rate of about 3 cubic centimeters per minute. When the ammonium thiocyanate was completely added, the mixture was refluxed for about 30 hours. The reaction medium was then poured out of the flask and dried at C. for 20 hours. The triethylene diamine salt of dithiocyanic acid was obtained.

Example 4 The methyl triethylene diamine salt of thiocyanic acid was prepared by adding 129.3 grams (1.02 mols) of methyl triethylene diamine and 154.3 grams of distilled water to a one liter three-neck flask equipped with a magnetic stirring bar, a stopper and a thermometer well. 0.2 gram of dibutyl phthalate was placed in the thermometer well to facilitate heat transfer.

78.1 grams (1.03 mols) of NH SCN were dissolved in 101.9 grams of distilled water and added to the flask from a beaker. The beaker was then rinsed with 56.7 grams of distilled water, which was added to the flask.

The resulting mixture was refluxed for approximately 6 hours. At the end of the 6 hour period the reaction medium was filtered and dried in an oven at 105 C. to obtain the methyl triethylene diamine salt of thiocyanic acid.

Analytical data Theoretical (percent): C, 51.89; N, 22.70; H, 8.11; S, 17.30. Actual (percent): C, 50.8; N, 22.76; H, 8.12; S, 18.6.

Example 5 The methyl triethylenediamine salt of thiocyanic acid was prepared by dissolving 63 grams (0.5 mol) of methyl triethylenediamine in 100 grams of hexane. 38 grams (0.5 mol) of NH SCN crystals were added to the hexane solution with stirring. The crystals slowly changed in appearance to a yellow, soft, curdly, gelatinous solid.

The product mass was allowed to stand for 72 hours after which the hexane was poured off and the product dissolved in a 3 to 1 mixture of isopropanol and water. The solvent was then evaporated and 82 grams (99% yields) of product were recovered.

Example 6 The 2-ethyl-4-methyl imidazole salt of thiocyanic acid was prepared by adding 55 grams (0.5 mol) of 2-ethyl-4- methyl imidazole to a flask equipped with a thermometer, a reflux condenser and a magnetic stirrer. 145.1 grams of distilled water were added to the flask. 38.1 grams (0.5 mol) of ammonium thiocyanate dissolved in 55.4 grams of distilled water were then added slowly to the flask and the reaction mixture was refluxed for 15 hours. At the end of the reflux period, the solution was poured into an evaporating dish and placed in an oven at 210 F. After 3 hours the temperature was raised to 250 F. and held at this higher temperature for 2 hours. 81.5 grams of the 2-ethyl-4-methyl imidazole salt of thiocyanic acid were obtained.

Analytical data Theoretical (percent): C, 49.68; H, 6.52; N, 24.84; S, 18.94. Actual (percent): C, 49.55; H, 6.67; N, 25.45; S, 18.9.

Example 7 The methyltriethylene diamine salt of hydrobromic acid was prepared by placing 344 grams of hexane and grams of methyltriethylene diamine (0.99 mol) in to a 1 Analytical data Theoretical (percent): C, 40.60; H, 7.30; N, 13.50; Br, 38.50. Actual (percent). C, 39.69; H, 8.00; N, 13.45; Br, 38.86.

Example 8 The monohydrobromic acid salt of 2-ethyl-4-methyl imidazole was prepared by adding 162 grams of xylene to a 500 cc. flask together with 55 grams of 2-ethyl-4-methyl imidazole (i.e., approximately 0.48 mol) To this solution, 85 grams of 48% hydrobromic acid were added to the flask in 20 gram increments until all of the hydrobromic acid had been added. The mixture was stirred for one hour and then the water layer, containing the product, was placed in an evaporating dish.

Analytical data Theoretical (percent): C, 37.34; H, 6.74; N, 14.50; Br, 41.48. Actal (percent): C, 36.70; H, 5.88; N, 14.52; Br, 42.90.

Example 9 The mono para-toluene sulfonic acid salt of triethylene diamine was prepared by first dissolving 17.2 grams of para-toluene sulfonic acid in 150 grams of benzene. 11.2 grams of triethylene diamine were dissolved in 80 grams of benzene and the combined benzene mixtures were allowed to sit for 3 days as the product precipitated out. The product was then dried and identified as the mono paratoluene sulfonic acid salt of triethylene diamine.

Example 10 The monohydrobromic acid salt of triethylene diamine was prepared by dissolving 112 grams of triethylene diamine and 200 grams of distilled water. 167 grams of 48% hydrobromic acid solution was then added and the resulting salt was dried at 110 C. The product was identified as the monohydrobromic acid salt of triethylene diamine.

Example 11 The 2-ethylhexoic acid salt of triethylene diamine was prepared by adding 147.7 grams of 2-ethylhexylic acid (1.03 mols) to a three-neck flask equipped with a reflux condenser. 112 grams of triethylene diamine (1 mol) were then added to the flask and the mixture was heated to 60 C. The resulting solution turned dark brown and the product was identified as the 2-ethylhexoic acid salt of triethylene diamine.

Example 12 The 2-ethyl-4-methyl imidazole salt of acetic acid was prepared by dissolving 55 grams (0.5 mol) of 2-ethyl-4- methyl imidazole in 200 cubic centimeters of acetone. A mixture of 30 grams (0.5 mol) of acetic acid in 100 cubic centimeters of acetone was slowly added to a flask containing the 2-ethyl-4-methyl imidazole.

The resulting reaction mixture was stirred periodically for 4 hours. After standing for 24 hours, the reaction product was separated from the hexane and dried to obtain the desired salt.

1 By difference.

-In the following examples, the epoxy formulations were evaluated in the following manner: First, the epoxy resin and the curing mixtures were chilled overngiht at 40 F. in separate sealed bottles. The next day the two components were mixed together by hand-stirring with a metal spatula for 7 to 8 minutes. The completely mixed formulation was returned to the refrigerator for 30 to 45 minutes residence time, after which it was cast onto glass plates that had been sprayed with a fluorocarbon release coating. The low temperature films were returned to the refrigerator and, later, were periodically checked for tack free time.

The tack free test was performed as follows: A finger was pressed onto the surface of the curing film with moderate pressure for a couple of seconds, after which it was removed. If the finger came away without any pull being felt, that time was recorded as the tack free time. Thus, the tack free time is a measure of gel time.

Tack free times were also determined using Federal Specification Test 14121-4061. This test requires an aluminum strip 1" x 3" with a 1" x 1" square touching the film. The remaining 1" x 2" strip is bent as a side arm at such an angle so as to just balance a 5 gram weight. The film is said to be tack free when the side arm falls immediately after a 300 gram weight standing on the 1" x 1" square for 5 seconds is removed.

The rate of cross-linking was determined by measuring the film hardness using graded drawing pencils in accordance with known practice in the paint field. The gradations were as follows: 6B (softest), 5B, 4B, 3B, 2B, B, HB, F, H, 2H, 3H, 4H, 5H, 6H, 7H, 8H, 9H (hardest).

Other tests included solvent and acid resistance tests which determined the amount of solvent or acid absorbed or extracted in a particular period of time. For example, in the solvent weight gain test the amount of solvent (xyleneisopropanol in a 1:1 ratio by Weight) which is absorbed after a 24-hour or longer immersion period is measured.

Example 13 Formulation A and formulation B were prepared from 50 parts of Araldite 507, 50 parts of Araldite 6005, and 18.5 parts of Hardener 956. In addition, one part of 2- ethyl-4-methyl imidazole and 5 parts of the thiocyanic acid Isgalt of triethylene diamine were added to formulatlon Formulations A and B were evaluated and the results of these evaluations are set forth below:

Tack free time:

Iliours, g 61-54 23 ours, 7 3 Pencil hardness:

2 days, 3237 F 6B 1 B 4 days, 3237 F 4B F-H 2 days, room temperature. H H Shore D hardness:

2 days, 32-3? F 21 51 4 days, 3237 F 32 70 2 days, room temperature- 66 73 1 Surface tacklness observed.

Example 14 These formulations were evaluated and the results of the evaluations are shown below:

Tack free time, hours; 35-40 F -19 8-11. Pencil hardness:

2 days, 35-40 F F F. 7 days, 35-40 F. l 2H 3H. 2(1855, R'I1 H 2H. 10 7 days. RT L 3H 311. Chemical resistance, percent weight gain after immersion in a 1:1 mixture of xylene-isopropanol:

Cured 7 days, 40 F 78.7 86.9. Cured 7 days, RT 1 10.8 12.4 Chemical resistance, percent weight gain after immersion of 10% acetic acid: Cured 7 days, 40 F 13.4 33.2 10 Cured 7 days, RT 1 18.7 28.0. Sand filled composition; trowellability Good Ease of casting Good Do. Adhesion:

Steel do.. Do. Concrete Cured 7 days at 77 F 14,000 12,000. Top coat residual surface tack:

Cured 7 days, 40 F Severe Cured 7 days, RT 1 .do.

1 Room temperature. 2 Very goo n0 3 Concrete broke before epoxy pulled away. 0 4 Very slight.

Example 15 Formulation A was prepared from 100 parts of Araldite 471X75, 5.6 parts of methyl n-propyl ketone, 9.4 parts of Hardener 955, 17.2 parts of methyl alcohol, 7.2 parts of 2-nitropropane, 4.8 parts of the triethylene diamine salt of thiocyanic acid and 0.4 part of 2-ethyl-4- methyl imidazole.

A second formulation B was prepared from 100 parts of Araldite 471-X75, 5.6 parts of methyl n-propyl ketone, 34.3 parts of Pentamid 815 and 14.7 parts of xylene.

The evaluation of the resulting clear epoxy coatings is set forth below:

Gloss-:

Cured 7 days at 75 F 100+ 100+ Cured 7 days at 37 F 100+ 100+ Pencil hardness:

Cured 7 days at 75 F 3H F Cured 7 days at 37 F H B 05 Sward hardness:

Cured 7 days at 75 F 26 20 Cured 7 days at 37 F 10 2 Abrasion resistance, liters of sand/mil of film removed:

Cured 7 days at 75 F 25-30 53-58 Cured 7 days at 37 F 16-18 0 Adhesion Scotch Tape, number of squares retained:

Cured 7 days, 75 F 100 0 Cured 7 days, 37 F 100 100 Knife, 10 best:

Cured 7 days, 75 F 8 4 Cured 7 days, 37 F 6-8 2 Impact resistance (inch pounds) direct:

Cured 7 days, 75 F 14 22 6o Cured 7 days, 37 F 7 Reverse:

Cured 7 days, 75 F 4 25 Cured 7 days, 37 F 2 1 Film too soft to test.

Example 16 Identical flooring compositions A and B were prepared containing 200 parts of Araldite 507, 56 parts of Hardener 955, 2 parts of 2-ethyl-4-methyl imidazole and 1000 parts of sand. In addition, formulation A contained 12.2 parts of the triethylcne diamine salt of thiocyanic acid and formulation B contained 16.2 parts of the dithiocyanic acid salt of triethylene diamine.

These formulations were evaluated and the results of the evaluation are set forth below:

Tack free time (hours):

40 F., -75% R.H. 28-30 20-23 73 F., -50% H.1 1 5.7 2+ Shore D hardness (73 F. and 50% R.H. after 72 hours) 83 82 Compressive strength at 40 F. (p.s.i.):

days 870 315 2,040 1,200 3, 200 2, 000 4, 700 4, 930 8, 560 7, 800 9, 800 6, 200 Chemical resistance, percent weight absorbed after 24 hours immersion; cured 14 days at 73 F. and 50% R.H.:

Distilled Water 1. 24 2.11 10% HCl l 2.02 2. 69 10% H2804 1. 98 2. 79 10% HNOa 2. 84 2. 75 10% NaOH 2. 02 2. 89 10% acetic acid 8. 47 16. 2 methyl ethyl ketone 17.1 15. 3 Xylene:isopropanol 5. 34 18. 5 Cured 14 days at 40 F. and 75% R.H.:

Distilled water 1.02 1. 90 HCl 1. 15 2. 64 2. 04 3.04 1. 32 2. 29 1. 41 1. 64 10% acetic acid 15.1 17. 2 Methyl ethyl ketone 8. 91 8. 31 Xylenedsopropanol 19. 7 10. 5

1 R.H.=Relative humidity.

Example 17 Identical formulations, A and B, were prepared containing 100 parts of Araldite 507, 31.5 parts of Hardener 955 and 8.6 parts of Pentamid 840. 6.6 parts of the triethylene diamine salt of thiocyanic acid were added to formulation A. Formulation B contained 5.7 parts of triethylene diamine.

The evaluation of formulations A and B is set forth below:

1 Room temperature.

Example 18 Three formulations were prepared from similar compositions containing 100 parts of Araldite 6005, 28 parts of Hardener 95 5 and 1 part of 2-ethyl-4-methyl imidazole. Formulation A contained 4 parts of methyl triethylene diamine. Formulation B contained 8.1 parts of the dithiocyamc acid salt of triethylene diamine (prepared in accordance with Example 3). Formulation C contained 6.1 parts of the monothiocyanic acid salt of triethylene diamiue (prepared in accordance with Example 1).

1 1 The evaluation of Formulations A, B and C is set forth in the following table:

Solvent resistance, percent Weight gained after 7 days immersion in 1 to 1 xylenezisopropanol mixture (cured 7 days):

40 F 75% R.H.

52.1 53. 2 58.4 73 F., 50% 11H. 40. 1 54. 45. 8 Solvent resistance, percent weight extracted during 7 days immersion in 1 to 1 xylene:iso propanol mixture (cured 7 days):

40 F., 75 R.H. 11 2 16.7 73 F., 50% R.H. 3 4 7.3 4. 2 Acetic acid resistance, percent weight gained after 7 days immersion in acetic acid (cured 7 days):

F., 75% R.H. 34. 1 21. 4 33.0 73 F., R.H. 32.8 22. 8 24.9 Acetic acid resistance, p ex ng zidasgs immersion in 10% acetic acid (cured 7 avs 40 F., R.H. +7.4 +3.5 +5.0 73 F., 50% R.H. +6.9 +4.2 +4.8

1 R.H.=Reiative humidity. 2 Unable to weigh sample.

Example 19 parts of Araldite 6005, 28 parts of Hardener 955, 4 parts of methyl triethylene diamine and 1.6 parts of the 2-ethyl-4-methyl imidazole salt of acetic acid (prepared in accordance with Example 12) were blended together as a control for a similar blend of 100 parts of Araldite 6005, 28 parts of Hardener 995, 4 parts of methyl triethylene diamine and 1.6 parts of the 2-ethyl-4-methyl imidazole salt of thiocyanic acid (prepared in accordance with Example 6).

These formulations were then evaluated as maintenance coatings. In the following table the formulation prepared with the acetic acid salt is labeled as A and the formulation prepared with the salt of thiocyanic acid is labeled as B.

Example 20 Five formulations (formulations A through E) were prepared from 50 parts of Araldite 507, 50 parts of Araldite 6005 and 18.4 parts of Hardener 956. Formulation B also contained 0.6 part of water. Formulations C, D and E also contained 1 part of 2-ethyl-4-methyl imidazole and 5 parts of the thiocyanic acid salt of triethylenediamine. In addition, formulations C, D and E contain water in the amount of 0.3 part, 0.6 part and 0.9 part, respectively.

Formulations A through E were evaluated and the re sults of these evaluations are set forth below:

A B C D E Tack free time:

2 days, HB HB B F F 7 days, 35 F"... H F H H H 2 days, RT HB H H 2H 3H 7 days, H H 2H 2H 2H Chemical resistance percent weight gain after 7 days immersion xylene-isopropanol:

Cured 7 days, 35 F 38. 9 36.1 12. 6 30.5

Cured 7 days, RT 15. 3 13. 23 18.3

1 Surface exudation, moderate.

2 Surface exudation, severe.

3 Sample highly swollen and discolored.

4 Sample damaged during experiment, unable to weigh.

NOTE.-RT Room temperature.

Example 21 Three formulations were prepared each employing 100 parts of Araldite 507. The first formulation (formulation A) also contained 23 parts of Hardener 956. Formulation B contained 18.4 parts of Hardener 956, 5 parts of the triethylene diamine salt of thiocyanic acid, 1 part of 2-ethyl-4-methyl imidazole and 0.6 part of water. Formulation C contained 18.4 parts of Hardener 956, 5 parts of the triethylene diamine salt of thiocyanic acid, 1 part of 2-ethyl-4-methyl imidazole and 2.4 parts of water.

These formulations were evaluated and the results of the evaluations are shown below:

A B C Tack free time; hours, 35 F 02+ 18-22 22-25 Pencil Hardness:

4 days, 35 F B H H 7 days, 35 F. F 211 F 4 days, RT. H H 7 days, RT"... 2H 3H 311 Chemical resistance,

days immersion xyiene-isopropanol:

Cured 7 days, 35 F 45. 4 36. 7 Cured 7 days, RT 28.1 17.8 10% acetic acid:

Cured 7 days, 35 F 218. 7 87. 1 Cured 7 days, RT 29. 2 48. 7 47. 1

1 Severe amine blush. 2 Moderate amine blush. 3 Slight amine blush. 4 Sample disintegrated during test;

N oru.-RT= Room temperature.

Example 22 Compressive strength, p.s.i..... A B

Cured days at 37 42 F.:

Example 23 A formulation was prepared containing 100 parts of Araldite 6005, 28 parts of Hardener 955, 1 part of 2-ethyl- 4-met'hyl imidazole and 6.6 parts of the tertiary amine salt prepared in accordance with Example 7.

13 This formulation was evaluated and the results of the evaluation are shown below:

Tack free time:

A formulation (A) was prepared by blending 100 parts of Araldite 6005, 28 parts of Hardener 955, 4 parts of methyltriethylene diamine, 1.8 parts of 2-ethyl-4-methyl imidazole and 1 part of the monoacetic acid salt of methyltriethylene diamine.

A second formulation (B) was prepared by blending 100 parts of Araldite 6005, 28 parts of Hardener 955, 4 parts of methyltriethylene diamine, and 1.6 parts of the tertiary amine salt prepared in accordance with Example 8.

These formulations were evaluated and the results of the evaluations are shown below:

Tack free time:

ours, 40 F 25 13 Hours, R. T 1 7 8 Pencil hardness:

8 hrs., 40 F 2B 413 hrs., R. T. F F 7 days, 40 F F 2H 7 days, H 3H Solvent weight gain percent:

Cured 7 days, 40 F 29. 6 25. 8 Cured 7 days, R. T. 26. 1 23. 2 Solvent weight loss percent:

Cured 7 days, 40 F Cured 7 days, R. T. 2. 8 11. 3

1 R. T.=Room temperature.

Example 25 A formulation was prepared by blending 200 parts of Araldite 507, 56 parts of Hardener 955, 2 parts of Z-ethyl- 4-methyl imidazole, 1000 parts of sand and 18.2 parts of the tertiary amine salt prepared in accordance with Example 11.

This formulation was evaluated and the results of the evaluation are set forth below:

From the foregoing it will be seen that this invention is well adapted to obtain all of the ends and objects hereinabove set forth, together with other advantages which are obvious and which are inherent to the system.

Thus, a low temperature epoxy curing system is provided by the present invention in which certain tertiary amine salts of hydrobromic acid, paratoluene sulfonic acid, Z-ethylhexoic acid or thiocyanic acid act to accelerate epoxy curing agents in a manner such that epoxy resins are cured at a practical and acceptable rate at temperatures as low as 35 F. It has been shown that the low temperature epoxy curing system of the present invention can be used advantageously for epoxy maintenance coating and flooring applications. Extremely rapid curing is obtained when either triethylene diamine or methyl triethylene diamine is used as the tertiary amine in the accelerator and including 0.3 to 2.4 parts of water per hundred parts of resin with the accelerator in the curing system. It has also been found that the rate of curing ob tained using the epoxy curing system of the present invention can be improved by the addition of 2-ethy1-4-methyl imidazole in an amount between 0 and 5 parts per hundred parts of resin. Another feature of the present invention is the relatively low dermatitis hazard present with the use of the curing system.

What is claimed is:

1. A curing system for epoxy resins comprising a mixture of the tertiary amine salt of hydrobromic acid, paratoluene sulfonic acid, 2-ethyl-hexoic acid or thiocyanic acid and an epoxy curing agent wherein the tertiary amine is triethylene diamine, methyl triethylene diamine or 2- ethyl-4-methyl imidazole and the curing agent is at least one member of the group consisting of a modified liquid amidoamine, having an equivalent weight in the range of 65 to 90, and a viscosity in centipoises at 25 C. in the range of 150 to 900; a low viscosity, modified amine having an amine nitrogen value percent in the range of 23.5 to 27 and a viscosity in centipoises at 25 C. in the range of 300 to 600; and a polyamide, having an amine value in the range of to 400, and a viscosity in poises in the range of 7-12 at 150 C. to 75030' at 40 C.; the weight ratio of the tertiary amine salt to curing agent being from about 0.01:1 to 0.73:1.

2. The curing system of claim 1, in which the tertiary amine is triethylene diamine and additionally containing between 0.3 and 2.4 parts of Water per hundred parts of the resin.

3. The curing system of claim 1, in which the tertiary amine is triethylene diamine and additionally containing between 0.4 and 0.9 part of water per hundred parts of the resin.

4. The curing system of claim 1, in which the tertiary amine is methyl triethylene diamine and additionally containing between 0.3 and 2.4 parts of water per hundred parts of the resin.

5. The curing system of claim 1, in which the tertiary amine is methyl triethylene diamine and additionally containing between 0.4 and 0.9 part of water per hundred parts of the resin.

6. The curing system of claim 1, which includes 2-ethyl- 4-methyl imidazole in an amount in the range of 0 to 5 parts per hundred parts of resin.

7. The curing system of claim 1, in which the tertiary amine salt is triethylene diamine and the epoxy curing agent is an amide-amine.

8. The curing system of claim 7, in which the mixture is present in a solvent blend of nitropropane and methanol in the approximate ratio of 2:1.

9. The curing system of claim 1, in which the tertiary amine salt is the thiocyanic acid salt of triethylene diamine and which contains 5 to 10 parts of a polyamide of less than about 70 poises at 40 C. per parts of resin.

(References on following page) References Cited UNITED RICHARD D. LOVERING, Primary Examiner STATES PATENTS I. GLUCK, Assistant Examiner Loefiier 2602 EC Warren 260-2 EC Garnish 2602 EC 5 2602 EC, 2 N, 45.9, 501.1, 583 R May et a1. 2602 N UNITED STATES PATENT OFFICE CERTIFICATE 6F CQRRECTWN Patent No. 42,649 Dated February 1 s 101? Inventor(S) Harold A. Green and Robert GPPet-rel 1 a It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 63 "dematitis" should read dermatitis Column 2, line 69, "Viscosity. poises" should read Viscosity, Poises Column 3, line 5, "trademark. Araldite" should read trademark Araldite Column 3, line 17, "characteristics." should read characteristics:

Column 7, line 31, "Actal" should read Actual Column 8, line 43, "18.5" should read 18.4

Column 10, line 58, "1=1" should read 1:1 Column 11, line 38, "995" should read 955 This certificate supersedes Certificate of Correction issued December 26, 1972.

Signed and sealed this 13th day of March 1973.

(SEAL) Attest:

EDWARD M.FLlE'1'CIIER,JR. I ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents F ORM PO-105O (IO-69) USCOMM-DC 6O376-P6E:

* U.5. GOVERNMENT PRINTING OFFICE: 1969 036 3334,

was UNITED STATES PATENT OFF-ICE "CERTIFICATE OF CORRECTIQN Patent No. 3,6 2,6 l9' a d February 15, 1972 Inv n I Harold A. Green and Robert G. Petre-lla It is certified that error appears in the above-identified-patent 4 and that said Letters Patent are hereby correeted as shown below:

Column 1, line 63 "dermatitis" should read dermat1tis- Column 2, line 69 "Viscosity. poi'ses" should read- Viscosity, Poises Column 3, line 5 "trademark. Araldite" should read -'.-trademark Ar'aldit'e-- Column 3, line 17 "characteristics." should. read --char'acteristics:--

Column 7, line 31 "Aot l" should read --Actual-- Column 8, line 43 "18.5" Should read --18.'u--

Column 10, line 58 "i=1" should read --1=1-- Column ll, line 38 "995" should read --955-- Signed end sealed this Z6th day of December 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Commissioner of Patents Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,642,649 Dated February ls 1 1'77 Inventor(s) Harold A, Green and Robert G l Pecrel 1 a It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 63 "dematitis" should read dermatitis Column 2, line 69, "Viscosity. poises" should read Viscosity, Poises Column 3, line 5, "trademark. Araldite" should read trademark Araldite Column 3, line 17, "characteristics." should read characteristics:

Column 7, line 3l,"'Actal" should read Actual Column 8, line 43, "19.5" should read 18.4 Column 10, line 58, "l=l" should read lzl Column 11, line 38, "995" should read 955 This certificate supersedes Certificate of Correction issued December 26, 1972.

Signed and sealed this 13th day of March 1973.

(SEAL) Attest:

EDWARD M.FL13TCIIER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents F PC4050 USCOMM-DC 60376-P89 k U.S. GOVERNMENT PRINTlNG OFFICE? 959 0-365-334. 

